A critical step involves interacting with her while she sleeps; you must "remove the sheet" at least once at night to trigger a middle-of-the-night event involving a spy at the window. Mikasa Ackerman :

If you are reading this, you have already accepted your fate. Not the fate of dying in the jaws of a Titan, but the fate of fighting back. The mobile game Attack on Survey Corps (often abbreviated as AOTSC ) is notorious for its punishing difficulty curve, unforgiving gas management, and split-second combat timing. Many players quit after the "Trost Gauntlet" mission. This exclusive walkthrough will not only help you clear the game—it will help you dominate it.